I. Field
The present invention relates generally to communication, and more specifically to techniques for performing acquisition by terminals operating in a power save mode.
II. Background
Wireless communication systems are widely deployed to provide various types of communication services such as voice, packet data, and so on. These systems may be multiple-access systems capable of supporting communication with multiple users by sharing the available system resources. Examples of such multiple-access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, and frequency division multiple access (FDMA) systems. A CDMA system may be designed to implement one or more standards such as IS-2000, IS-856, IS-95, and W-CDMA. A cdma2000 system is a CDMA system that may implement IS-2000 and/or IS-856. A TDMA system may be designed to implement one or more standards such as Global System for Mobile Communications (GSM). A GSM system may implement General Packet Radio Service (GPRS) for packet data transmission. These various standards are well known in the art.
Some wireless communication systems (e.g., those that implement IS-2000, W-CDMA, and GSM/GPRS) are capable of supporting voice and packet data services. Each type of service is characterized by a particular set of requirements. For example, voice service typically requires a fixed and common grade of service (GOS) for all users and further imposes relatively stringent and fixed delays. In contrast, packet data service may be able to tolerate different GOS for different users and may further be able to tolerate variable amounts of delays. To support both types of service, a wireless communication system may first allocate system resources to voice users and then allocate any remaining system resources to packet data users who can tolerate longer delays.
Some wireless communication systems (e.g., those that implement IS-856) are optimized for packet data transmission, which is typically characterized by long periods of silence punctuated by large bursts of traffic. For an IS-856 system, a large portion of the system resources may be allocated to a single user, thereby greatly increasing the peak data rate for the user being served.
A service provider/network operator may deploy multiple wireless communication systems to provide enhanced services for its subscribers. For example, a service provider may deploy a voice/data system (e.g., an IS-2000 system) capable of providing both voice and packet data services for a large geographic area. This service provider may further deploy a packet data system (e.g., an IS-856 system) capable of providing packet data service for “hot spots”, which are areas where packet data usage is expected to be high. The coverage areas of the two systems would typically overlap, and these systems would then be considered as “overlay” systems. A multimode/hybrid terminal may then be able to receive service from one or both of the systems depending on its location and the desired service.
If a terminal is mobile, then it may move into and out of the coverage areas of the individual systems as it roams about. One of the challenges when operating in such overlay systems is determining when to attempt acquisition of the packet data system when under the coverage of the voice/data system. Each unsuccessful acquisition attempt of the packet data system consumes battery power, which then reduces battery life and standby time. When idle, the terminal may be operated in a power save mode whereby power consumption is minimized to the extent possible so that standby time may be extended. In the power save mode, it is desirable to attempt acquisition on the packet data system in a manner such that battery power is conserved while maximizing the likelihood of acquisition.
There is therefore a need in the art for techniques to efficiently perform acquisition by a terminal in a wireless communication system.